Wai Tsang thought he had committed the "perfect murder"

A “cold and calculated” scientist who bludgeoned his ex-wife to death was caught after his satnav revealed his true movements.

Wai Tsang, 33, plotted the “perfect murder” of Mingzi Yang, 29, with whom he was involved in a custody battle over their five-year-old son.

A jury heard he created what he thought was a “cast-iron alibi” that placed him 40 miles from the Lincoln murder scene by claiming that he had driven directly from his home in Grimsby to go mountain biking in Sherwood Forest.

He switched off his mobile phone so the signal could not be traced and got coffee and parking receipts to prove he had been there.

Miss Yang’s fiancé, Darren Grundy, 32, who found her body, was instead arrested and held by police for three days.

However, Tsang, a chemistry graduate who worked as an industrial hygienist, agreed to hand police the satnav from his Mazda estate car which had recorded his every movement.

Instead of driving directly to Sherwood Forest, it revealed that he had actually driven into Lincoln, parking in a lay-by outside the city for two and a half hours.

He then cycled to his Miss Yang’s home, waited for her to return from the morning school run and battered her to death.

Lincoln Crown Court heard that detectives found CCTV footage of Tsang cycling to and from the murder scene wearing a distinctive blue helmet. A witness also came forward to say they saw a cyclist matching Tsang's description outside the scene of the murder.

Traces of Miss Yang’s blood were also found on Tsang’s bicycle and his watch.

Wau Tsang created what he thought was a 'cast iron alibi' (Lincolnshire Police)

Tsang, who is British and of Chinese origin, denied murdering Miss Yang on June 17 but was found guilty after a month-long trial.

Judge Michael Heath jailed him for life on Monday and ordered him to serve a minimum of 28 years.

The judge said: “You are a very intelligent and very clever man. When poor Darren Grundy, a wholly innocent man, was in custody for three days I have no doubt that you thought you had committed the perfect murder and got away with it.

“You are a cold, calculating individual and a liar but you didn't fool the jury as you mendaciously attempted to explain away the constellation of compelling evidence that the prosecution produced.”